A valve apparatus that opens/closes a tubular member that forms an exhaust gas flow path for exhaust gas from an internal combustion engine is known (see Patent Document 1). This valve apparatus disclosed in Patent Document 1 is disposed downstream of an exhaust gas inflow section in the exhaust gas flow path in the tubular member, and comprises a valve seat and a valve. The valve seat is shaped like a diffuser, having its downstream-side diameter expand in the exhaust gas flow path. The valve engages with the valve seat via a buffer that is disposed on an inner circumferential surface of the valve seat.